Insulating board of fibrous glass and method and apparatus for making same



Aug. 11, 1964 L. J. PLUMBERG ETAL INSULATING BOARD OF FIBROUS GLASS AND METHOD AND APPARATUS FOR MAKING SAME 2 Sheets-Sheet 1 Filed Oct. 18. 1957 Aug 11, 1964 L. J. PLUMBERG ETAL. 3,144,376

INSULATING BOARD oF FIBRoUs GLASS AND METHOD ANDAPPARATUS FOR MAKING SAME Filed Oct. 18. 1957 2 Sheets-Sheet 2 757 W g//S lNvENToRs L gama Ko J. FLuM Bex@ BY /1 u GLLST THEKOFF United States Patent O lNSULATlNG BOARD F FIBRGUS GLASS AND METHOD AND APPARATUS FUR MAKING SAME Leonard I. Plumberg, Kansas City, Mo., and August C.

Thero, Kansas City, Kans., assignors to Gwens- Corning Fiberglas Corporation, a corporation of Delaware Filed Oct. 18, 1957, Ser. No. 691,085 8 Claims. (Cl. 161-156) This invention relates to an insulating board composed principally of bonded fibrous glass and to such a board primarily intended for roof insulation. More specifically the invention pertains to an insulating board having a fibrous glass panel as a base to which a covering of sheet material is adhered. The invention further relates t0 methods and apparatus for producing such insulating boards.

insulating boards of this invention are designed mainly for flat or low-pitched roof decks that are to be surfaced with a built-up bitumen-bonded roofing where they may be laid over any type of deck including wood, steel, concrete or precast slabs. However, boards of this invention may be employed to advantage for insulation in other areas such as walls and floors.

For many years procedures for constructing built-up roong remained unchanged and comprised simply the application of alternate layers of bitumen and roofing felts. Greater strength, and permanence was secured mainly through increasing the number of layers. This construction has served quite satisfactorily from a waterproofing and weathering standpoint but is strikingly deficient in its insulating capacity.

With roofs of this type solar heat is transferred readily to the interio-r of buildings to aggravate working condiitons in hot hummer months. Another very objectionable consequence of the absorption of heat by the roof is the liquefaction and drippage of bitumens of low melting points down between roofing boards and through other cracks or apertures in the roofing deck. The heat further encourages the formation of blisters by expanding air pockets and moisture trapped within the body of the roofing structure.

Also, the chilling of such a roof at night or in cool weather causes air borne moisture within the building to condense upon the ceiling area promoting mildew, rot, rust and other water induced deterioration as well as to precipitate upon machinery or material.

The need of better insulating qualities in built-up roofing installations was finally met by introducing therein a stratum of material with high resistance to the passage of heat. The most effective composition of such insulating bodies has proved to be fibrous glass. The multitude of minute air cells within glass fiber masses are responsible for their insulating superiority. Thinner layers of such fibrous glass products may be utilized with performance equal to that of layers of the best competitive substances at least one third greater in thickness.

In spite of the great importance of these modern thermal barriers, they have been looked upon as a rather alien constituent by the roofing trade, to be endured rather than welcomed, as adding difiiculties to installation procedures without contributing to overall improvement of the roofing structure.

Because of the nature of the work, involving the heating, transport, and deposition of high temperature bitumens, the attendant activity is under pressure by the time element, messy and not conducive to a care taking attitude. The comparatively soft insulating boards, while sufficiently strong to withstand reasonable loads, are subject, whether or not protected by overlying roofing felts,

to deformation under the load of gravel-carrying wheelbarrows or other heavy installation equipment. Also, the boards through their compressibility allow rupturing of overlying felt surfacing strata by mishandling of edged or pointed tools. These injuries are apt to occur whether or not plank runways are utilized and other precautionary steps are taken.

Accordingly, in spite of the otherwise exceptional qualities of fibrous glass insulating boards including low thermal conductance, light weight, and chemical stability, they share with other insulating materials a compression strength below that desirable, from a practical standpoint, in a roofing component.

It is the prime object of this invention to provide a fibrous glass insulating board that possesses improved resistance to compression loads and to sharp blows of a fracturing nature.

A concomitant purpose of this invention is to provide an insulating board that amplifies the overall strength of a built-up roof structure.

A further aim of this invention is the provision of an insulating roofing element which presents a strong, impermeable surface for receiving a mopping of hot bituminous material.

More specically, an object of the invention is the creation of a fibrous glass insulating board having a smooth covering sheet preferably of kraft paper adhered to a bonded glass fiber panel core by a film of asphalt with the sheet strengthened through the embedding in the asphaltic film of continuous or connected fibrous glass elements such as strands, yarn, matt, scrim or fabric.

Another purpose of this invention is to provide methods and apparatus for producing fibrous glass insulating boards of the nature portrayed in the preceding objects.

The achievement of the objects of this invention is derived in part from the provision of a fibrous glass insulating board having an impervious covering of sheet material adhered through the medium of a glass ber reinforced asphaltic film to the upper surface of a base panel of bonded fibrous glass.

The objects of the invention are further realized through the herin disclosed methods and apparatus whereby a bonded fibrous glass panel is employed as a base, a sheet product is coated with an asphalt film, a continuous fibrous glass component is embedded in the film, and the coated sheet is wrapped around or laid on one face of the base panel with the coated side of the sheet in adhering contact with the base panel.

In practicing this invention, a pack of glass fibers, impregnated with a heat settable binder, is collected upon a receiving conveyor. The binding agent is set while the pack is held to a desired thickness and density. The dimensionally stabilized pack is then trimmed along its edges to a standard width and carried past a covering sheet delivery station. This preferably involves a compartment below the path of the pack wherein there are a sheet feeding device, coating equipment for applying an asphaltic film to one side of the sheet, and devices laying upon the film a continuous form of fibrous glass such as strands, yarns, or a bonded mat. A second coating of asphalt is then projected upon the fibrous glass elements. The coated sheet is introduced under and against the traveling pack to which it is adhered by setting of the asphaltic constituent through cooling thereof or by the evaporation of the volatile vehicle in which it may be dissolved or suspended.

Further details of the methods, apparatus and products of this invention as well as alternate forms thereof are set forth in the following description and explained in connection with the accompanying drawings in which:

FIGURE 1 is a diagrammatic, vertical and longitudinal section of aY glass fiber or glass wool production line incorporating equipment for producing fibrous glass insulation boards according to this invention;

FIGURE 2 is an elevational view, partly in section, of an apparatus for applying an asphalt coating to a sheeting material and incorporating within the coating a fabric of fibrous glass;

FIGURE 3 is an enlarged, sectional view taken in the direction of the arrows from the line 3 3 of FIGURE 1, of the portion of the apparatus pertaining to the coating and delivery of the covering sheet;

FIGURE 4 is a perspective view with parts broken away of a fibrous glass insulating board embodying this invention; and

FIGURE 5 is a broken, perspective view of a section of a built-up roofing incorporating insulating boards of this invention.

Referring to the drawings in more detail, the glass wool production line illustrated in FIGURE 1 begins with the glass melting tank 2, from the forehearth 3 of which, the molten glass ows in fine streams from orifices in bushings 4. The molten threads of glass are drawn downwardly and attenuated by the blast of air or steam jets discharged from manifolds 6. These fibers are preferably, but not necessarily, between thirty and sixty, hundred thousandths of an inch in diameter.

As the fibers, in comparatively short lengths, fall within hood 8 toward the receiving conveyor it) discrete particles of an uncured binding agent, preferably a phenol formaldehyde solution extended with twenty percent Vinsol, a rosin suspension, are introduced into the mass of fibers by spray nozzles 12 projecting through the end wall of the hood 8. Vinsol is a natural product derived from the steam distillation of pine wood. The binder may be used in sufficient quantity to constitute approximately nine percent by weight of the fibrous glass pack formed on conveyor after curing of the binder.

The conveyor 10 is foraminous and may be a woven wire belt type. The accumulation of the binder impregnated fibers in a layer or pack upon conveyor 1t) is aided by a flow of air down through 'the conveyor into suction chamber 14 from which it is exhausted through outlet 15 by a suitable blower.

The fibrous pack 16 thus formed has in this instance a density of one and a quarter pounds per cubic foot, an effective width of four feet and a thickness of eight inches. The latter dimension is controlled by the speed of the conveyor and the fiber production rate. For purposes of this discussion the conveyor speed is at the rate of sixty feet per minute.

The continuous fibrous pack 16 is advanced upon receiving conveyor 10 for delivery to conveyor 18, which is preferably an apron type with perforated metal slats 19 extending between side roller chains 20. The latter extend around sprockets 21 and 22. Conveyor 1S carries the pack through the binder curing oven 23 wherein the pack is compressed to a one inch thickness by upper conveyor 24, which is similar in design to conveyor 18.

The binder is brought to a curing temperature by air driven into oven 23 by blower 26 and heated by passage over the electrical heating elements 27 in air inlet duct 28. The perforated slats 19 of conveyors 18 and 24 provide paths for the air to reach and travel through the pack and then to the exhaust outlet 30 below the upper stretch of conveyor 18.

Upon leaving oven 23 the pack 16 is held to its compressed thickness of one inch and an accompanying density of ten pounds by the binder particles brought to a final set by the applied heat. In order to establish the width of the pack at a precise four feet and to square the sides, the edges are cut sharply by pairs of matched cutting discs 33 and 34.

Following the trimming action by discs 33 and 34, as the pack is transferred to the following conveyor 36, a web 38 is interposed beneath the pack. This web is brought up from the lower chamber or pit 4t) where it is produced from a base sheeting 41 drawn from a supply roll 42 by feeding rollers 44 and 45. The sheeting is preferably a strong, forty pound kraft paper, but may be composed of various other"`impervious materials including plastic films and filled, fibrous glass mats or fabrics. However, the kraft paper has ample strength for most purposes and is economical in cost. Racks 47 are provided for holding a reserve supply of rolls of the paper stock.

Through application cylinder Si), as shown both in FIGURE 1 and FIGURE 3, an asphaltic coating, approximating four ounces per square foot is laid upon the strip of sheeting held against the cylinder by roller 44. The elevating cylinder 51, partially submerged in the liquefied asphalt within tank 53, transfers a film of the coating to application cylinder 50. The asphalt is a high grade type, one favored by applicant having a melting point of approximately F. and maintained in tank 53 by heating elements 55 at a temperature above 300 F.

As the band of kraft paper with the hot film 56 of asphalt travels upwardly from around roller 44 continuous yarns, strands, or cords 57 of fibrous glass are projected into the asphaltic film by a row of air induction guns 58. The string-like fibrous glass elements are drawn from stationarily mounted bobbins or spools 59. A yarn having a weight of one pound per fifteen thousand yards is consideredvery suitable and is applied at a rate between two to eight grams per square foot, but preferably in a quantity resulting in a deposit of three grams per square foot. These quantities relate to boards for roof insulation. A much higher amount would be desirable in a board for wall siding. The induction guns 58 are suspended from a supporting bar 158 and receive air from a delivery pipe 159.

In order to insure thorough attachment of the composite web 3S founded upon the paper strip 41 to the compressed fibrous glass pack 16, with no interference from the interposed yarn, a hot asphaltic coating 68 is directed upon the yarn layer by a series of spray guns 61 supplied with atomizing air and asphalt, respectively, through lines 62 and 63. This asphalt is of the same quality as that supplied from tank 53, and likewise is preferably applied at a rate of four ounces per square foot.

The composite web 38 formed by the successive coatings on the base sheet 41 is then led by roller 64 beneath the advancing fibrous glass pack 16 as the latter reaches conveyor 36. The web is preferably about eight to ten inches wider than the pack, with equal portions extending from beneath opposite edges of the pack. These side extensions 38e of the web, as shown in FIGURE 3, are turned upwardly and over the borders of the pack and pressed in adhering contact by spiral guides 65.

If it is desired to huriy the cooling and hardening of the asphaltic component air may be directed against the lower side of the pack assembly 66 by nozzles 67 in a compartment 69. The pack with its integrated sheeting cover is then severed into sections by a rapidly moving guillotine or knife 71. This may be actuated to cut the pack at two foot intervals to produce boards 73 of the standard size of two by four feet.

An alternate arrangement for building the composite web or sheeting cover is shown in FIGURE 2. In the chamber 74 depicted therein the kraft paper strip 41 from supply roller 42 receives its first coating 56 of asphalt from a tank 79, through application and elevating cylinders 50 and 51, in the same manner as followed by the apparatus of FIGURES 1 and 3.

Instead, however, of having yarns of fibrous glass projected upon the initial hot asphaltic film, in this embodiment, a fibrous glass fabric band 84 is superimposed thereon. This may be woven cloth but is, preferably, in view of the cost factor, scrim or a bonded mat of fibrous glass. The mats may be secured in their sheet form by one of a variety of binders including starches, furfurals and polyesters. The fabric band 84 is drawn from a supply roll 86 into adhering contact with the coated paper strip 41 around the guiding roller 88.

A coating 91 of hot asphalt is then applied over the fibrous glass fabric 84 by a series of spray guns 61 positioned crosswise of the laminated web and receiving air and asphalt through lines 62 and 63. This asphaltic film, like that supplied from tank 79, should have a covering capacity of approximately four ounces per square foot of surface.

The laminated web 98 thus formed is directed upwardly over supporting cylinder 64 into cohering union with the bonded fiber pack 102. The resulting pack assembly 104 proceeds upon conveyor 36 for the subsequent edge turning of the web over the borders of the base pack and for the cutting of the final set pack into the desired sizes of insulating boards.

A perspective View of a portion of an insulating board S produced by the equipment depicted in FIGURES 1-3 is presented in FIGURE 4. As may be noted, the composite web or sheeting originally applied against the lower side of the fibrous glass pack becomes the upper surface of the finished product. Accordingly, over the basic fibrous glass panel 11) there is first an asphaltic layer 111 bond to the panel and also intimately adhering to the following overlay 112 of continuous or closely connected fibrous glass elements, which may be yarn or strand form or of a fabric nature. integral with the first asphaltic layer 111 through bridging portions reaching around and between the fibrous glass elements is the final asphaltic stratum 114.

Adhering to the final layer 114 of asphalt is the sheeting 116 preferably of tough kraft paper but which may be a durable, impervious film of plastic, bonded fibrous glass mat or other sheet stock. The laminated covering 11S, composed of the layers of asphalt, the ebedded glass elements and sheeting 116, is turned down around the ends of the basic fibrous glass panel 110 and lapped against the borders 119 of the underside of the panel.

In FIGURE 5 a perspective view of a broken portion of a built-up roofing illustrates the use of insulating boards of this invention in such an assembly. There are, of course, a great many forms of built-up roofings incorporating varying numbers and kinds of plies.

Over the concrete roof deck 121, as depicted in FIG- URE 5, is a sealing layer 123 of bituminous material. Shortly after this is mopped or otherwise spread upon the deck at the recommended rate of forty pounds per one hundred square feet and while it is still in a molten state, the insulaing boards 108 are successively pressed into this liquefied bitumen and fitted tightly against adjoining boards. The open face of each board is against the sealing layer 123. The boards are so laid that the joints between the boards in each row are offset from the joints between boards of adjacent rows. After the installation of the layer 124 of insulating boards has been completed a solid asphaltic covering 125 is applied, usually by mopping, at the recommended rate of thirty pounds per hundred square feet.

Where exceptionally high insulation is required multiple layers of the insulating boards, separated by such asphaltic moppings, may be employed, but as here illustrated, a ply of roofing felt 126 is the next component. This is followed by a bituminous coating 127, a second roofing felt 128, another bituminous layer 129, and a third final ply of roofing felt 13). An extra heavy coating 132 of bitumin, amounting to sixty pounds per hundred square feet, is then poured and spread over the final roofing felt layer 132. While this bitumen is still hot, four hundred pounds of gravel per one hundred square feet of area is embedded in it to form the finishing surface 134 of the built-up roofing.

During the installation of an extensive built-up roofing of the type pictured in FIGURE 5 there is considerable heavy traffic involving the moving of large bitumen heating equipment, application devices and material carriers,

the latter comprising drums of bitumens and wheelbarrows holding several hundred pounds of gravel. The loads and shocks associated with this rugged traffic are particularly dangerous in connection with a finished or semi-finished insulated roof as they may then puncture the waterproofing felt plies as well as depress the insulating members to a degree where they lose considerable insulating efficiency. Their insulating property is also weakened should fracture permit the entry of fiuid bitumens into the air pocketed interior of the insulating members.

The greatly increased strength of the membrane covering of insulating boards of this invention withstands compression stresses and rupturing impacts whereby the integrity and serviceability of the boards is maintained. This vigorous resistance to injury is derived not only from the composite covering but also from the intimate bond between the basic fibrous glass panel and the laminated covering. The coherence of the surface fibers of the panel with the adjoining asphalt film cooperates with the imbedded continuous or closely connected fibrous glass elements and the adhered top sheet of kraft paper to provide a strong, integral structure.

The assembly serves to hold in place and support overlying plies of roofing felts. With its high quality asphalt component and tough kraft surface it further provides an excellent mopping surface which is impervious and remains rigid under the heat of applied bitumens of lower melting points.

The strength of the top portion of these insulating boards also contributes to the overall toughness and waterproofing capacity of the built-up roofing to an extent equivalent to at least an additional ply of the best roofing felt. The laminated sheet covering, unattached to the basic fibrous glass panel and without the extra endurance derived from such attachment, is susceptible of great tension or strain without breaking. In fact, it is qualified to serve, in separate form, as a fiashing membrane, in which capacity a particularly high degree of strength is required. When so used, its construction may involve a filled fibrous glass mat in place of the kraft paper, and a heavy glass fiber screen product as the continuous fibrous glass elements embedded between the asphaltic films. One such screen product is well known under the trademark Glasfab.

For the purpose of presenting a clear and distinct disclosure the embodiments of the apparatus, methods, products and materials of the invention have been described in quite specific terms. However, it should be obvious that the invention may be practiced with a wide range of alternative means.

For instance, the fibrous glass pack is produced according to the description and drawings directly from a fiber forming hood. Instead of this procedure certain benefits would accrue from building the pack with preform stock. The latter is created by tearing apart and reassembling an original binder saturated pack.

Then, too, no reference has been made to the possibility lof utilizing other mineral wools, although it is well known that, while they are inclined to be of an inferior nature, for some purposes, they make a useable substitute for glass wool.

Phenol formaldehyde has alone been cited as a binding agent for glass fiber masses, but it has been Well established that other materials such as epoxy and melamine resins give excellent results. Also, the amount of the binder utilized may be varied within a range roughly of five to fifteen percent with the cost factor tending to discourage higher quantities and diminishing strength accompanying the use of lower amounts.

A compressed pack thickness of one inch and ten pounds per cubic foot density was chosen herein only as a typical example. Actually insulating roofing boards may vary in thickness from at least one-half to two and one-half inches and there is no serious handicap in having their densities range up to fourteen pounds. At the same time masses of fibers of the smallest diameters have greater strength, and with them, densities lower than ten pounds would be practical. In fact, from the standpoint purely of insulating value the optimum density is considered to be around five pounds per cubic foot.

In connection with the disclosed apparatus a single covering sheet or web is applied to the bonded fibrous pack extending completely over only one face thereof. For some situations a board covered on both sides would be desirable and this could be produced by laying upon the upper surface of the pack a composite sheet delivered from above the traveling pack. It would desirably have, in connection with the disclosed pack of a width of four feet, the same width so as not to overlap the edges of the pack. The composite sheet from below could then have its projecting edges turned over and down against the borders of the upper sheet and a tight seal obtained without interference from overhanging portions of the upper sheet. Such a board would contribute to the formation of a vapor seal beneath it in a built-up roofing assembly and would have strength to oppose vapor or air bubbles arising beneath it.

In the arrangements herein described the first asphaltic lm is applied by means of a rotating cylinder. For a heavier coating spray devices could be used for this purpose. They are preferably utilized for the second asphaltic coatings as there a roller coater would' be inclined to pick up the continuous, fibrous glass elements. While a particularly good quality asphalt is recommended for creating the composite web, lower melting point asphalts and even pitch products would perform fairly satisfactorily.

In briefly summarizing the attainments of the invention, it should be noted that an insulating board has been provided that has greatly improved power to bear compressing loads and disruptive impacts; also, that boards of this invention contribute to the waterproofing character and overall strength of a built-up roof structure.

In addition, the subject insulating boards present a particularly stout, impermeable surface for receiving a hot bituminous mopping.

Finally, the invention has provided apparatus and methods for readily constructing insulating boards of the superior qualifications, above recited.

We claim:

1. A thermal insulating roofing board including a base panel at least one half inch in thickness, said base panel comprising a highly porous, low density, substantially rigid body of mineral fibers, and a cured thermosetting binder dispersed through the body bonding the fibers together and holding the body to a definite thickness, said roofing board further including a distinct stratum of fibrous glass elements over the base panel, a covering sheet disposed over the stratum of fibrous glass elements, and a thermoplastic binder, in which the fibrous glass elements are completely embedded, said thermoplastic binder holding the fibrous glass elements in fixed position relative to each other and cohering the base panel, fibrous glass elements and covering sheet, said covering sheet being sufiiciently reinforced by said thermoplastic binder and fibrous glass elements to provide the roofing board with a tough, rupture and compression resisting surface.

2. A roofing board according to claim l in which the thermoplastic binder is an asphalt having a melting point of approximately 190 F.

3. A roofing board according to claim 1 in which the fibrous glass elements are generally continuous strands of multiple glass fibers disposed in a random arrangement.

4. A roofing board according to claim 1 in which the fibrous glass elements are comparatively short fibers disposed in angular relation in a common plane and primarily held in matted form by a binder distinct from the said thermoplastic and thermosetting binders.

5. A roofing board according to claim 1 in which the covering sheet is kraft paper.

6. A roofing board having a substantially rigid, porous body of mineral fibers bonded together by a cured thermosetting binder, said body having a density of not more than fourteen pounds per cubic foot, a strong, permeable, planar layer of fibrous glass elements superimposed upon the porous body, an outer, inherently fiexible and impervious covering sheet, and an asphaltic binder in which the glass elements are completely embedded, said asphaltic binder attaching together the porous body of mineral fibers, the layer of fibrous glass elements and the outer covering sheet and said covering sheet being stiffened and made highly resistant to rupture through the reinforcement of the asphaltic binder and glass elements.

7. The method of producing thermal insulating boards which comprises forming a continuous pack of mineral fibers impregnated with a heat settable binder, said pack being substantially thicker than two and one half inches and having a density substantially below five pounds per cubic foot, compressing the pack to the extent that the density thereof is increased to between five and fourteen pounds per cubic foot and the thickness is reduced to be- `tween one half and two and one half inches, applying heat to the pack to set the binder while the pack is cornpressed and thus dimensionally stabilizing and stifening the pack, moving said stabilized pack horizontally along a production line, feeding a strip of flexible sheeting in a path leading to the production line, applying a film of adhesive binder to one side of the strip of fiexible sheeting, embedding strong fibrous glass elements in the film, then pressing said side of the strip into cohering relation against the moving stabilized pack of mineral fibers, setting the adhesive binder to attach the strip to the pack, and finally cutting the pack with the attached strip into units of thermal insulating boards.

8. An apparatus for producing insulating boards including, in combination, a fibrous glass pack forming hood, a conveyor carrying the continuous formed pack from the hood, means feeding a flexible strip of sheeting in a path leading upwardly to the conveyor, a first coating device applying an adhesive film to the strip, means laying strong fibrous glass elements in the film, a second coating device applying an adhesive film over the fibrous glass elements, and means directing the strip in cohering relation against the underside of the pack of fibrous glass as it is carried by the conveyor, said first coating device, said means laying glass elements, and said second coating device being disposed in vertically sequential order below the conveyor.

References Cited in the file of this patent UNITED STATES PATENTS 2,295,971 Savidge Sept. 15, 1942 2,409,951 Nootens Oct. 22, 1946 2,457,784 Slayter Dec. 28, 1948 2,474,398 Heritage June 28, 1949 2,550,465 Gorski Apr. 24, 1951 2,552,124 Tallman May 8, 1951 2,577,205 Meyer et al. Dec. 14, 1951 2,599,625 Gilman et al. June 10, 1952 2,642,370 Parsons et al. June 16, 1953 2,704,734 Draper et al. Mar. 22, 1955 2,721,816 Wood Oct. 25, 1955 2,731,066 Hogendobler et al. Jan. 17, 1956 2,732,885 Hoven Jan. 31, 1956 2,744,044 Toulmin May 1, 1956 2,771,387 Kleist et al Nov. 20, 1956 2,790,741 Sonneborn et al. Apr. 30, 1957 2,830,648 Haddox Apr. 15, 1958 3,050,427 Slayter et al Aug. 21, 1962 

1. A THERMAL INSULATING ROOFING BOARD INCLUDING A BASE PANEL AT LEAST ONE HALF INCH IN THICKNESS, SAID BASE PANEL COMPRISING A HIGHLY POROUS, LOW DENSITY, SUBSTANTIALLY RIGID BODY OF MINERAL FIBERS, AND A CURED THERMOSETTING BINDER DISPERSED THROUGH THE BODY BONDING THE FIBERS TOGETHER AND HOLDING THE BODY TO A DEFINITE THICKNESS, SAID ROOFING BOARD FURTHER INCLUDING A DISTINCT STRATUM OF FIBROUS GLASS ELEMENTS OVER THE BASE PANEL, A COVERING SHEET DISPOSED OVER THE STRATUM OF FIBROUS GLASS ELEMENTS, AND A THERMOPLASTIC BINDER, IN WHICH THE FIBROUS GLASS ELEMENTS ARE COMPLETELY EMBEDDED, SAID THERMOPLASTIC BINDER HOLDING THE FIBROUS GLASS ELEMENTS IN FIXED POSITION RELATIVE TO EACH OTHER AND COHERING THE BASE PANEL, FIBROUS GLASS ELEMENTS AND COVERING SHEET, SAID COVERING SHEET BEING SUFFICIENTLY REINFORCED BY SAID THERMOPLASTIC BINDER AND FIBROUS GLASS ELEMENTS TO PROVIDE THE ROOFING BOARD WITH A TOUGH, RUPTURE AND COMPRESSION RESISTING SURFACE. 